Hypoxia in the Baltic Sea: Biogeochemical Cycles, Benthic Fauna, and Management |
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Authors: | Jacob Carstensen Daniel J Conley Erik Bonsdorff Bo G Gustafsson Susanna Hietanen Urzsula Janas Tom Jilbert Alexey Maximov Alf Norkko Joanna Norkko Daniel C Reed Caroline P Slomp Karen Timmermann Maren Voss |
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Institution: | 1. Department of Bioscience, Aarhus University, Frederiksborgvej 399, 4000, Roskilde, Denmark 2. GeoBiosphere Science Centre, Department of Geology, Lund University, S?lvegatan 12, 223 62, Lund, Sweden 3. Department of Biosciences, Environmental and Marine Biology, ?bo Akademi University, 20500, Turku, Finland 4. Baltic Nest Institute, Stockholm University, 106 91, Stockholm, Sweden 5. Department of Environmental Sciences, Aquatic Sciences, University of Helsinki, PO BOX 65, 00014, Helsinki, Finland 6. Institute of Oceanography, University of Gdansk, al. Marsza?ka J. Pi?sudskiego 46, 81-378, Gdynia, Poland 7. Faculty of Geosciences, Utrecht University, Budapestlaan 4, 3584 CD, Utrecht, The Netherlands 8. Zoological Institute, Russian Academy of Sciences, Universitetskaya nab. 1, 199034, St. Petersburg, Russia 9. Tv?rminne Zoological Station, University of Helsinki, J.A. Palméns v?g 2600, 10900, Hanko, Finland 10. Leibniz-Institute of Baltic Sea Research, IOW, Seestr. 15, 18119, Rostock, Germany
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Abstract: | Hypoxia has occurred intermittently over the Holocene in the Baltic Sea, but the recent expansion from less than 10 000 km2 before 1950 to >60 000 km2 since 2000 is mainly caused by enhanced nutrient inputs from land and atmosphere. With worsening hypoxia, the role of sediments changes from nitrogen removal to nitrogen release as ammonium. At present, denitrification in the water column and sediments is equally important. Phosphorus is currently buried in sediments mainly in organic form, with an additional contribution of reduced Fe-phosphate minerals in the deep anoxic basins. Upon the transition to oxic conditions, a significant proportion of the organic phosphorus will be remineralized, with the phosphorus then being bound to iron oxides. This iron-oxide bound phosphorus is readily released to the water column upon the onset of hypoxia again. Important ecosystems services carried out by the benthic fauna, including biogeochemical feedback-loops and biomass production, are also lost with hypoxia. The results provide quantitative knowledge of nutrient release and recycling processes under various environmental conditions in support of decision support tools underlying the Baltic Sea Action Plan. |
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Keywords: | Climate change Ecosystem recovery Ecosystem services Eutrophication Nutrient management Regime shift |
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